1. Field of the Invention
The present invention relates to a sheet-like thermal sensing element, a temperature sensor, a temperature controller and a sheet-like heater.
2. Description of the Background Art
Various sheet-like heat generating elements have conventionally been developed. Especially, the sheet-like heat generating elements which use the carbon fiber mixed paper have attracted special interest recently. The temperature of such a sheet-like heat generating element depends on the position on the heat generating surface. Accordingly, temperatures in a plurality of positions on the heat generating surface must be detected when controlling the temperature of the sheet-like heat generating element. Examples of conventional temperature sensors are shown in FIG. 7, FIG. 8 and FIG. 9.
FIG. 7 shows a thermistor. This thermistor 101 includes a glass case with diameter of about 2 mm and a pair of lead wires. The thermistor 101 has excellent thermal responsiveness but it can sense the temperature in a point or a line.
FIG. 8 shows a thermal sensing wire. This thermal sensing wire 102 is made of platinum wire, nickel wire or the like of diameter about 0.1 mm. The thermal sensing wire 102 is linear in shape so that it can sense heat in a large area, but it has inferior thermal responsiveness because of its large mass.
FIG. 9 shows a thermostat. This thermostat 103 includes a package which is a rectangular prism 10 mm wide, 20 mm long and 3 mm thick, for example, and a pair of lead wires. This thermostat senses only predetermined temperature and has extremely inferior thermal responsiveness, therefore it can be used only for over-heat preventing.
The thermistor 101 shown in FIG. 7 can sense the temperature only in the point or in the line. Accordingly, a plurality of thermistors 101 must be attached to the heating surface of the sheer-like heat generating element in order to detect the temperature of the sheet-like heat generating element and control the temperature thereof. In this case, the interconnections are complex and the size of the sheet-like heat generating element will become large because of provision of the thermistors.
The thermal sensing wire 102 shown in FIG. 8 has a large mass, so that its thermal responsiveness is bad. Accordingly, it has difficulty in accurately controlling the temperature of a sheet-like heat generating element such as the carbon fiber mixed paper having very high temperature rising rate.
The thermostat 103 shown in FIG. 9 can sense the temperature only in a point similarly to the thermistor 101, so that a plurality of thermostats are needed in order to detect the temperature of the sheet-like heat generating element. Accordingly, the interconnections must be complex and the sheet-like heat generating element will be large in size.